The present invention relates generally to machines for popping popcorn, and more particularly to an improved kettle for popping popcorn.
To obtain the highest quality popped corn, that is, popcorn having a large size and a fluffy texture as a result of having a high expansion ratio, it is imperative to closely control the cooking time of the popcorn. If the cooking time is too fast or too slow, the resulting popcorn will be small and chewy, and there will be too many unpopped kernels. To effectively control the cooking time of popcorn popped in a kettle, the heat energy input into the kettle must be closely controlled.
Present electric popcorn popping machines utilize tubular or ring type heating elements made from nickle-chromium wire and having a magnesium oxide outer layer for insulation. These heating elements are clamped to the bottom of popcorn popping kettles to transfer heat by conduction to the cooking surface of the kettle. Large size kettles may have as many as two or three individual heating elements. These current popcorn popping machines suffer many drawbacks, such as exhibiting hot and cold spots on the cooking surface of the kettle, where areas near the heating elements are hotter than areas which are further away from the heating elements. Variations in the thermal profile of the cooking surface are also partly related to the conductivity of the kettle material. From a maintenance standpoint, the most desirable kettle material is stainless steel, which provides a durable cooking surface that is easily cleaned. However, stainless steel has a lower thermal conductivity value than low carbon steel or aluminum, and therefore produces very uneven surface temperatures when heated by conventional tubular or ring-type heating elements.
Another drawback of conventional popcorn popping machines is that a significant amount of heat energy is lost below the heating elements by radiation and convection. This loss of heat energy translates to an inefficient cooking process. Current popcorn popping machines also exhibit a significant response time lag between the instant power is supplied or discontinued to the heating element and the actual heat transfer from the element to the popcorn popping kettle. This time lag is due to the mass and construction of the tubular or ring type heating elements and is particularly troublesome when power is shut off to the heating element, but the kettle continues to receive heat energy from the heating elements.
For at least these reasons, a need exists for an improved popcorn popping kettle which can provide a uniform heating of a cooking surface, and in particular, a stainless steel cooking surface, without exhibiting hot or cold spots, and which has a reduced response time, compared to current popcorn popping machines, to provide efficient and controlled cooking of popcorn.
The present invention provides an improved popcorn popping kettle having a heater which provides for uniform heating of the entire kettle cooking surface to ensure controlled cooking of the popcorn. The kettle heater is a thick film heater which can generate heat when supplied with electric current. As referred to herein, the term xe2x80x9cfilmxe2x80x9d and xe2x80x9cfilm heaterxe2x80x9d are directed to heating elements or resistive conductors which are relatively thin with respect to their possible length and width dimensions. Such films may be printed, plated, or otherwise deposited on the surface to be heated. Therefore, such heated films are generally considered to be two-dimensional heaters, although they do have a certain finite thickness, as will be understood by persons skilled in the art. Film heaters suitable for an embodiment of the invention might be referred to as xe2x80x9cthick film heatersxe2x80x9d because the films are relatively thicker than thinner films used in other industries and applications, such as the semiconductor industry. However, relative to existing heating elements and heaters for prior art popcorn popping machines, the films and heaters of the present invention are significantly thinner than the heating elements used and taught by that art.
The film of the present invention may be applied directly to the kettle cooking surface or it may be applied to a substrate which is thermally coupled to the kettle. An insulating material may be applied between film and substrate to provide electrical separation of kettle and film. The film heater may be constructed to provide a substantially uniform temperature across the cooking surface or it may be designed to provide a controlled temperature gradient, as may be desired in some applications.
In another aspect of the invention, a popcorn popping machine is constructed with a kettle including a film heater coupled to the kettle according to the principals of the present invention. In accordance with yet another aspect of the present invention, a method for cooking popcorn in a popcorn popping machine includes the steps of introducing popcorn into a kettle constructed with a film heater and controlling the heat energy of the kettle to correspond to the optimum cooking time of the popcorn.
Accordingly, the present invention provides a thick film heater for a popcorn popper, which overcomes the drawbacks of prior art popcorn poppers which utilized conventional tubular or ring type heating elements. For example, the thick film heater of the present invention provides for uniform heating of the cooking surface of a popcorn popping kettle and delivers heat to the kettle in a more efficient manner than was possible with conventional heating elements. Furthermore the thick film heater of the present invention exhibits a reduced response time with respect to power supplied to the heater, to provide better control of the heat energy delivered to the kettle. These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and description.